This study aims to produce a relative sea-level database for the English Channel and Atlantic coasts of France. Data collected from 54 research papers were reassessed by using SLIP methodology in order to propose a reliable reconstruction of Holocene relative sea-level rise. From 451 radiocarbon-dated sediment records, 264 index points were produced covering the last 11,000 years. The database is subdivided into nine regions along the coast. The post-glacial relative sea-level rise shows: (i) a decreasing of the rates of change over the time especially from 7-6,000 cal. yr BP; (ii) the linear rates of relative sea-level rise did not exceed 1 mm/yr from 7-6,000 cal. yr BP to present; (iii) the relative sea-level has never risen above present (0 m); (iv) no significant sea-level oscillations during the Holocene. Despite the high number of sea-level records available, the number of reliable data is still low and limits the quantification of isostatic trends. Nevertheless, the database should prove to be a valuable resource to researchers working on coasts of mesotidal to macrotidal environments of France and Atlantic Europe.

Holocene coastal dune formation under a continuously rising sea level (SL) is an abnormal response to increasing storm frequency. The aim of this work is to understand the coastal sedimentary budget and the present-day sand starvation, controlled by climate and man. Dating in Brittany shows that Aeolian deposition initiated from ca. 4000 cal BP, with the slowing down of the SL rise. Pre-historical dunes appeared here from ca. 3000 cal BP, without SL regression. After, further building phases recycled the same stock of sands. Historical dunes I developed from ca. 350 AD. Major storms between 900 and 1200 AD resulted in the construction of washover coastal ridges, the Historical dunes II. A part of the sand was evacuated offshore. From ca. 1350 AD, the pre-existing ridges are reworked forming the Historical dunes III, leading to rapid coastal erosion and inland drift. Holocene dunes with a rising SL constitute a temporary anomaly, mostly forced by man, soon erased by storms in Brittany.

With respect to others European oceanic facades, the Holocene relative sea-level (RSL) changes along the French Atlantic coasts have received relatively little attention. Even if it received some attention for geophysical modelling (Van de Plassche, 1991; Lambeck, 1997; Leorri et al., 2012), only two field-based studies really dealt with this subject in Western Brittany, agreeing on an oscillatory RSL pattern with a conspicuous pluri-metre negative variation occurring around 3000 BP (Morzadec-Kerfourn, 1974; Stephan, 2011). This paper is the first step on the way to update Western Brittany Holocene RSL data. It presents a new long-term Holocene RSL reconstruction based on basal peat deposits, compaction-free deposits that have been accumulated on top of the Pleistocene formations during the early-Holocene stages of the post-glacial transgression. Data used for the sea-level reconstruction are both new data and previously published datasets we have reassessed. New cores, extracted along the FinistÃ¨re peninsula in the framework of a coastal risk assessment research program, allowed us to collect new stratigraphic data. Dates initially published on basal peat deposits in previous studies (Morzadec-Kerfourn, 1974) were re-assessed through the same process to allow their incorporation in a combined dataset. In the absence of microfossils in most of our deposits, an alternate approach was used to determine the salinity regime of the basal peat deposit environments through the use of stable carbon isotope ratios and the observation of macro-botanical remains: brackish peat deposits were used as sea-level index points, while freshwater ones provided only high-limiting constraints. Eight new radiocarbon datings were obtained. A total of six new sea-level index-points and six new limiting points allowed us to derivate the long-term (millennial) changes in RSL in Western Brittany. A comparison of these data with some foraminifera-based regional RSL data shows that both data sets closely match. Altogether, the combined data show the RSL bending ca. 7000 and 3000 cal. BP, indicating progressively decreasing rising rates. Further work is needed to fill the centennial to pluri-centennial gaps that remain to ascertain potential periods of stability or strong decrease in the rising rates of the RSL ca. 6200 Â± 500 and 3000 Â± 500 BP.

In order to reconstruct former sea-levels and to better characterize the history of Holocene salt-marsh sedimentary infillings in West Brittany (western France), local foraminifera-based transfer functions were developed using weighted-average-partial-least-squares (WAPLS) regression, based on a modern data set of 26 and 51 surface samples obtained from salt-marshes in the bay of Tresseny and the bay of Brest, respectively. Fifty cores were retrieved from Tresseny, Porzguen, Troaon and Arun salt-marshes, which were litho- and biostratigraphically analysed in order to reconstruct palaeoenvironmental changes. A total of 26 AMS 14C age determinations were performed within the sediment successions. The Holocene evolution of salt-marsh environments can be subdivided into four stages: (i) a development of brackish to freshwater marshes (from c.â€‰6400 to 4500â€‰cal. a BP); (ii) salt-marsh formation behind gravel barriers in the bay of Brest (from 4500 to 2900 cal. a BP); (iii) salt-marsh erosion and rapid changes of infilling dynamics due to the destruction of coastal barriers by storm events (c.â€‰2900âˆ’2700â€‰cal. a BP); (iv) renewed salt-marsh deposition and small environmental changes (from 2700 cal. a BP to present). From the application of transfer functions to fossil assemblages, 14 new sea-level index points were obtained, indicating a mean relative sea-level rise of around 0.90Â±0.12â€‰mm aâˆ’1 since 6300 cal. a BP.